This invention relates to a forming apparatus for bending sheet metal into a variety of different cross-sectional shapes having a plurality of sheet contours included in each shape, and more specifically to an apparatus for forming corrugated metal sheets into pipe culverts of non-circular cross-section.
Machines for bending sheet metal into tubes or other shapes have been used for many years and are well known. Companies such as the Stamco Division of Monarch Machine Tool Co., located in New Bremen, Ohio, have been manufacturing forming apparatus for bending plain or corrugated sheet metal into cylindrical configurations, known as "cans," for more than 50 years. The typical can is formed of a single curved sheet or, for cans of a larger diameter, a plurality of curved sheets joined together.
In a conventional apparatus for forming metal cans, a sheet of plain or corrugated metal is passed between a pair of rolls, often called pinch rolls, which guide and drive the sheet as it progresses through the apparatus. A forming or buttress roll is located downstream in the apparatus and provides the proper degree of curvature to form the sheet metal into the can, or portion of the can, of a desired diameter. An example of a similar apparatus employing three rolls for metal bending, although not specifically for sheet metal, is U.S. Pat. No. 965,171. After the metal is rolled, two edges are joined to form a length of metal pipe. Conventional means of spot welding or riveting may be used.
Often, however, a user desires to change the shape of the formed pipe after it has been made to accommodate different liquid flow characteristics or adapt the pipe to fit particular specifications calling for pipe which is other than circular. A common example is "pipe arch" often used as highway culverts and shown and discussed, for example, in "Handbook of Drainage And Construction Products," published by Armco Drainage and Metal Products, Inc., Middletown, Ohio, in 1958 and in preceding and succeeding years.
Pipe arch and other pipe shapes have, in the past, been formed in one of two manners, both starting with a length of circular pipe. The first, and most common, is formation of the pipe arch in an apparatus which has exterior forming dies conforming to the desired ultimate shape of the pipe arch. A length of circular pipe is placed in the pipe arch device and the device then closed to squash the circular pipe, conforming it to the shape of the arching dies. Other manufacturers have used internal dies which are expanded within the circular pipe to deform it into the desired configuration. A serious deficiency of this type of equipment is the need for a separate set of dies for each size of pipe arch to be manufactured, and therefore the encumbent substantial cost. A further disadvantage is that it is not uncommon for localized excessive bending (creasing or kinking) to occur with the result that the galvanizing is broken loose in those locations.
Another disadvantage with the prior art methods of forming contoured pipe is encountered when it is necessary to join several lengths of the pipe to form a long culvert, etc. The pipe arch, or other non-circular shape resulting from the forming procedure, is not identical every time. Thus, often a series of cans so formed do not align properly and are difficult, if not impossible, to properly join.
An automatic machine for roll forming of metal parts is disclosed in U.S. Pat. No. 3,955,389. This machine continually senses the contour of the emerging portion of a part being formed, compares the emerging coutour with that desired, and continuously permits alteration of the forming operation to compensate for metal springback. The disclosed machine and process provides continuous "after-the-fact" monitoring to see that tolerances, which are critical in the aircraft industry, are closely met. Similar machines are disclosed in U.S. Pat. Nos. 3,906,765 and 4,047,411.
The automatic machines described in the foregoing patents, however, are highly complex and, consequently, expensive to construct and maintain. Thus, although they possibly are suitable for industries requiring close tolerances and therefore relatively expensive per part costs, they are not suitable for formation of more durable and less expensive products of lesser tolerance requirements, such as culvert pipe.
A substantial deficiency of the prior art in general has been the lack of a simple and effective machine for automatically and continuously producing a curved metal sheet of a plurality of sheet contours which is able to sense the distance the sheet being formed has travelled and, at discrete travel positions, effect changes in the degree of curvature impressed into the sheet. Automatic controls for other applications, such as those for numerically-controlled machine tools, are complex and not adaptable without excessive cost and ingenuity to control apparatus such as the above-discussed U.S. Pat. No. 3,955,389.
Other advantages of the disclosed embodiment are: the system is immune to electrical "noise" resulting from the fact that it requires continuous parallel data; and the drive of the rolling machine can be stopped and temporarily reversed during the process of rolling a sheet since the counters employed will count either up or down.